This invention relates to time determination and, in particular, to an apparatus and method for determining an indication of the current absolute time after an undetermined period of time in which accurate timekeeping is not possible.
Communication systems that are remote from each other frequently use antennas to exchange communications. Many of these antennas are designed to have narrow beamwidths so that sufficient power can be transmitted to other communication systems. Thus, properly aligning the antennas for remotely located communication systems is important so that the communication systems can continue to exchange communications. Maintaining this alignment, however, is difficult if the communication systems move relative to each other, which often occurs in space applications, unless each communication system can determine the relative position of the other communication system.
Fortunately, such determinations are readily known to those skilled in the art for space applications because the movement of objects, such as satellites and planets, in space is well understood. Of course, determining the current position of a communication system depends on first determining what is the current absolute time. For instance, if a communication system cannot determine what is the current absolute time, it would not be able to determine its position and, accordingly, how to orient the system antenna.
During most operations, however, it is relatively easy for a communication system to determine the current absolute time. For example, during periods in which a first communication system is in contact with a second communication system, the second communication system receives updates from the first communication system as to the current absolute time. Also, the second communication system may possess a relative time scale clock that allows a determination of elapsed time while out of contact with the first communication system.
A problem arises, however, when the communication systems are not in contact and there are undetermined periods of time when the communication system clock does not function properly. This occurs, for example, during a Martian winter, when it can be impossible to sustain clock operations due to extremely cold temperatures. Of course, when the temperature rises, the system clock becomes functional and communication is again possible, but only if the position of the communication system can be determined for reestablishing antenna orientation by means of a clock that can compute absolute time.
Hence, a clock that can be reset following a power outage or extreme environmental conditions would be highly desirable.
The present invention reduces or eliminates at least some of the problems and disadvantages associated with previous clocks. The present invention provides an apparatus and method for determining an indication of the current absolute time after an undetermined period of time in which accurate timekeeping is not possible.
In certain embodiments, the present invention provides an absolute time scale clock. The clock includes a radioactive isotope and a computer, which includes a processor and a memory. The processor can determine an indication of the current absolute time, and the memory can store a decay constant of the isotope, a reference time, and an amount of the isotope at the reference time. The clock also includes a supply of energy for supplying power to the computer. The clock further includes a detector positioned to respond to radioactive emissions from the isotope by generating an indication of the number of emissions over a time interval, the indication varying with said decay rate of said isotope. The processor, when supplied with sufficient power by the energy supply, is responsive to the indication from the detector, the decay constant, the reference time, and the reference amount to determine the indication of the current absolute time.
In other embodiments, the present invention provides a method for determining an indication of absolute time after an undetermined period time in which accurate timekeeping is not possible. The method begins with storing in a computer, before an undetermined period of time in which accurate timekeeping is not possible, a decay constant for a radioactive isotope, a reference time, and an amount of the isotope at the reference time. The method then calls for detecting an indication of loss of accurate timekeeping. After this, the method requires detecting an indication of the availability of accurate timekeeping after the undetermined period of time. Next, the method requires determining, after said undetermined period of time, the current decay rate of the radioactive isotope. Finally, the method calls for determining an indication of the current absolute time based on the current decay rate, the decay constant, the reference time, and the reference amount.
The present invention can provide a variety of technical features and advantages. For example, because the present invention can determine an indication of the current absolute time after an undetermined period of time during which accurate timekeeping is not possible, the invention is useful for determining time in environments where electrical activity is insufficient to support accurate timekeeping for an undetermined period of time. Moreover, the invention is useful for determining time in environments where electrical energy is insufficient to support accurate timekeeping for an undetermined period of time. Thus, time sensitive equipment operating in these types of environments can still function properly.
Other technical features and advantages will be readily apparent to those of skill in the art from the following figures, description, and claims.